1. Field of the Invention
The present invention relates to an optical disk driving apparatus, an optical disk driving method and an optical disk apparatus. The present invention can be applied to the adjustment of a disk tilt in case of recording or reproducing information recorded on, for example, an optical disk (MO), a compact disk (CD), a compact disk recordable (CD-R) or a digital video disk (DVD) serving as a disk-shaped recording medium.
2. Description of the Related Art
In the present optical disk field, there exist optical disks of not only the conventional CD format but also various formats such as a compact disk recordable (CD-R) coated with a color film of organic color, a magnetic disk (MO), a phase change optical disk (DVD-RAM).
A recording and reproducing apparatus for such optical disks controls a radial tilt angle indicating the radial gradient of an optical disk with respect to a light spot applied from an optical pickup. As recording density increases, demand for accurately detecting the radial tilt (radial warp) of an optical disk, controlling the radial tilt of the optical disk and thereby ensuring reliability, rises.
To satisfy the demand, the development of an optical disk recording and reproducing apparatus having a tilt mechanism for automatically adjusting the tilt of an optical pickup to accurately read a reproduction signal installed therein is underway. If the radial tilt of an optical disk is to be detected in the optical disk recording and reproducing apparatus of this type, a tilt sensor utilizing, for example, a reflection type sensor is mounted on an optical pickup and the sensor detects a radial tilt based on the difference in the quantity of reflected light when the optical pickup is moved in the radial direction of the optical disk. Then, the tilt mechanism using a DC motor is employed to control the tilt of the optical disk so as to minimize an error signal caused by the tilt of the optical disk from the tilt sensor.
There is also developed an optical disk apparatus which does not include a tilt sensor, processes a readout signal of an optical pickup and controls the tilt of the optical disk.
Japanese Patent Unexamined Application Publication No. 8-255360 discloses an optical disk apparatus for detecting a reflected light from an optical disk by means of two photo-detector elements to generate a difference signal, sensing an envelope of the detection signal to thereby detect differential components and conducting tracking control based on the differences to thereby remove DC offset.
Japanese Patent Unexamined Application Publication No. 9-212891 discloses an optical head apparatus which divides a laser light into a main light flux and a sub-light flux, individually generates push-pull signals from these light fluxes and generates a tilt signal corresponding to a disk tilt from these push-pull signals. Further, Japanese Patent Unexamined Application Publication No. 9-245357 discloses a servo control apparatus for an optical disk recording and reproducing apparatus, which apparatus converts a push-pull signal and a phase difference detection signal into a de-tracking signal and a radial tilt signal and controls a tracking servo and a thread servo.
FIG. 12 shows a conventional disk drive mechanism having a tilt mechanism using a tilt sensor.
In FIG. 12, the disk drive mechanism comprises a spindle chassis 202 made of a plate frame having an opening portion of generally rectangular shape provided therein, a pickup chassis 203 made of a plate frame which is slightly smaller than the spindle chassis 202 and which has an opening portion provided therein, and a tilt operation mechanism 204 rocking the pickup chassis 203 relative to the spindle chassis 202 based on the rotating force of a motor. The pickup chassis 203 is provided with a pair of shaft portions 203a protruding to both sides of the chassis 203 in width direction. The spindle chassis 202 is provided with a pair of bearing portions 202a rotatably supporting the shaft portions 203a. The combination of the paired bearings 202a and the paired shafts 203a supports the pickup chassis 203 to be rockable to the spindle chassis 202 in longitudinal direction.
The tilt operation mechanism 204 is provided on one longitudinal side of the spindle chassis 202. When the tilt operation mechanism 204 operates, the pickup chassis 203 rocks in the longitudinal direction of the spindle chassis 202. A spindle motor 205 is fixed to the other longitudinal side of the spindle chassis 202 in a state in which the rotary shaft of the motor 205 is directed upward. A turn table 206 onto which an optical disk is installed is attached integrally with the rotary shaft of the spindle motor 205.
Further, a guide shaft 203b and a guide portion which is not shown in FIG. 12 are attached parallel to the pickup chassis 203 at a predetermined distance between the guide shaft 203b and the guide portion to extend longitudinally. The slide member 208 of an optical pickup unit 207 is slidably supported by the guide shaft 203b and the guide portion. A rack which is not shown in FIG. 12 is fixed to the slide member 208. A gear positioned at the distal end portion of a head feed mechanism 209 is engaged with the rack. By driving the head feed mechanism 209 and transmitting the rotating force of the mechanism 209 to the slide member 208, the optical pickup unit 207 is moved to approach and separate from the turn table 206.
A tilt sensor 210 which detects a distance to the information recording surface of the optical disk installed onto the turn table 206, is mounted on the slide member 208. The tilt sensor 210 emits a light toward the information recording surface and detects the warp of the optical disk reflected by the information recording surface. Based on the detection result of the tilt sensor 210, the tilt operation mechanism 204 controls the optical disk so as to minimize an error signal caused by the warp of the optical disk. By doing so, the tilt of the pickup chassis 203 is modified and the tilt of the optical axis of the optical head 207a of the optical pickup unit 207 with respect to the tilt of the information recording surface of the optical disk can be adjusted. If the tilt sensor 210 is used, the mechanism 204 controls the optical disk so as to minimize an error signal from the tilt sensor 210 which signal is caused by the tilt of the optical disk. Thus, there is no need to know a tilt operation neutral point (mechanical center which will be referred to as xe2x80x9cmecha-centerxe2x80x9d hereinafter).
In the above-stated conventional optical disk recording and reproducing apparatus utilizing the tilt sensor, the tilt sensor and a DC motor for tilt operation are mounted on the optical pickup. Due to this, the conventional optical disk recording and reproducing apparatus has disadvantages in that production cost is pushed up and the optical pickup becomes larger in size.
Moreover, in an optical disk apparatus which does not include a tilt sensor and conducts tilt control by processing the readout signal of an optical pickup, when an optical disk for initiating the rotation of a spindle motor, is started, a reproduction signal cannot be read yet. Due to this, the quantity of the warp of the optical disk is not known and the optical disk is, therefore, required to be positioned at the tilt operation neutral point as the mecha-center in advance. If so, a sensor capable of obtaining the tilt operation neutral point is required. Besides, since a tilt operation angle is about xc2x1 one degree, the apparatus is disadvantageously required to have higher sensor attachment accuracy.
In addition, in the conventional disk drive mechanism having the tilt mechanism utilizing the tilt sensor shown in FIG. 12, the DC motor is used as a driving source of the tilt operation mechanism. The DC motor may be replaced by a stepping motor capable of conducting positioning control easily. The stepping motor is a kind of a synchronous motor. A magnetic field is continuously rotated by inputting a sine wave current and the synchronous motor thereby rotates. Since the stepping motor inputs a sine wave by dividing the wave into several steps, the magnetic field changes discontinuously and the motor repeats rotation, stop, rotation, stop . . . . As a result, large acceleration is generated every time the magnetic field changes discontinuously. And the above-stated tilt operation mechanism 204 operates, and a driving lever which is a cam piece which is not shown, provided on the pickup chassis 203 and abuts against a tilt cam cooperating with the tilt motor is repelled by the tilt cam. Due to this, when the pickup chassis 203 is rocked relative to the spindle chassis 202, the mechanical noise (which will be referred to as xe2x80x9cmecha-noisexe2x80x9d hereinafter) disadvantageously occurs. Also, because of the vibrated optical pickup, disturbance occurs to focus servo control and tracking servo control.
The present invention has been made in view of the above disadvantages. The object of the invention is to provide an optical disk drive apparatus, an optical disk driving method and an optical disk apparatus capable of reducing the occurrence of disturbance to focus servo control and tracking servo control.
To obtain the above object, an optical disk driving apparatus according to the present invention, having a tilt driving section on an optical disk for changing an incidence angle of a light spot applied from an optical pickup with respect to a rotating surface of an optical disk so as to record and reproduce information by applying the light spot by means of the optical pickup, is characterized in that the tilt driving section uses, as driving means, a stepping motor for changing an angle of the optical pickup with respect to the rotating surface of the optical disk and is provided with waveform shaping means for shaping a driving current waveform for driving the stepping motor.
Also, an optical disk driving method according to the present invention for changing an incidence angle of a light spot applied from an optical pickup with respect to a rotating surface of an optical disk so as to record and reproduce information in a tilt driving step by applying the light spot by means of the optical pickup, is characterized in that the tilt driving step comprises a waveform shaping step of shaping a driving current waveform driving a stepping motor, and a driving step of supplying the driving current waveform shaped in the waveform shaping step to the stepping motor serving as driving means and changing an angle of the optical pickup with respect to the rotating surface of the optical disk.
Further, an optical disk apparatus according to the present invention for changing an incidence angle of a light spot applied from an optical pickup with respect to a rotating surface of an optical disk by means of a tilt driving section, applying the light spot onto the optical disk by means of the optical pickup and thereby recording and reproducing information, is characterized in that the tilt driving section uses, as driving means, a stepping motor for changing an angle of the optical pickup with respect to the rotating surface of the optical disk and is provided with waveform shaping means for shaping a driving current waveform driving the stepping motor.
The optical disk driving apparatus, the optical disk driving method and the optical disk apparatus according to the present invention function as follows.
First, when a disk tray is moved forward, an optical disk is installed onto the disk tray. The disk tray is then moved backward while holding the optical disk. Thereafter, reproduction operation is designated by operating the operation section.
Since the tilt mechanism section employs a stepping motor serving as driving means for changing the angle of the optical pickup with respect to the rotating surface of the optical disk, the mechanism section can be moved to a tilt down maximum position and to a tilt up maximum position by driving the stepping motor by predetermined steps.
Here, since the initial position of the tilt operation is unknown, the tilt mechanism section is rotated by predetermined steps in the tilt up direction (or tilt down direction). At this moment, if the initial position is at the tilt minimum position, the tilt mechanism section reaches a tilt maximum position. Then, this tilt maximum position is set as a reference position and the mechanism section is rotated from this reference position in backward direction (tilt down direction) to a preset middle point by predetermined steps, whereby the optical pickup can be set at a tilt middle point.
Next, trial reproduction is performed. A jitter measurement circuit measures a jitter which is a fluctuation of a digital signal in time base direction during trial reproduction. The tilt motor driving circuit of the tilt mechanism section supplies a motor driving current to the tilt motor so that the jitter measured by the jitter measurement circuit becomes a minimum.
Here, for the purpose of smoothly rotating the tilt motor, in the tilt motor driving circuit, a rectangular driving current waveform is smoothly shaped by waveform shaping means. As a result, it is possible to ensure more accurate tilt control without mixing mechanical noise, the vibration of the optical pickup and the influence of disturbance to servo control into the jitter measurement result.
It is now assumed that the optical pickup is inclined in clockwise direction with respect to the rotating surface of the optical disk. In this state, if a jitter is detected from a reproduction signal of the optical disk, then the tilt motor is driven by the motor driving current corresponding to the rotation quantity at which the jitter becomes the minimum, the rotating force being transmitted to an optical pickup mounting surface and the optical pickup being inclined in counterclockwise direction. At this moment, the tilt motor smoothly rotates, so that the tilt of the optical pickup is smoothly adjusted. After performing tilt driving in this way, normal reproduction operation is started.